Respiratory Failure and VQ Mismatch

Hypoxia

Low PaO2

Hypercapnia

High PaCO2

Pulmonary Circulation Response to Low PaO2

Vasoconstriction

Systemic Response to Low O2

Dilation

Pulmonary Pressure and Resistance

Low-pressure, low -resistance

Systemic Pressure and Resistance

High pressure, High resistance

Pulmonary Vessel Structure

Thin walled, compliant arteries

Systemic Vessel Structure

Thick-walled, muscular arteries

Hydrostatic Pressure Gradient

Pressure caused by the weight of the blood itself in the blood vessels

Ventilation Perfusion Ration (V/Q)

Ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli

Normal V/Q

0.84

Effects of alveolar hypoventilation

Reduction in minute ventilation characteristically shows an increase in PaCO2. Results in CO2 retention.

V/Q local Regulation

Bronchioles dilate in response to raised PaCO2.

Arterioles constrict to low PaO2

Type 1 Respiratory Failure

Hypoxemia with a normal or low Co2

Type 2 Respiratory Failure

Hypoxemia with a high CO2

Normal PaO2 levels

11-15kPa

Normal PaCO2 levels

4.6-6.4kPa

Factors that affect diffusion

Partial pressure gradient

Gas Physical properties

Alveolar-capillary membrane

Reduced gas exchange area

Type 1 Respiratory failure value

<8kPa PaO2

normal/low CO2

Type 2 Respiratory failure value

<8kPa PaO2

>6kPa CO2

Which of these conditions is associated with Type 1 Respiratory failure?

Pneumonia

Which of these conditions is associated with Type 2 Respiratory failure?

Guillian-Barre syndrome

What flow happens in zone 1?

No blood flow

What flow happens in zone 2?

Intermittent blood flow

What flow happens in zone 3?

Continuous blood flow